1. Field of the Invention
The present general inventive concept relates to an image reading apparatus, and, more particularly, to an image reading apparatus capable of equally using a plurality of reading units to read image information from a document, and a method of controlling the same.
2. Description of the Related Art
An image reading apparatus reads image information recorded on a document and is mounted in a machine such as a scanner, a digital copier or a multi-function machine.
A method of reading both sides of a document in an image reading apparatus may be classified into two methods. One is a method of reading a first side of a transported document via a reading unit, changing a transport direction of the document via a document direction changing device, reversing the first side and a Second side of the document via a duplex path, and reading the second side of the document. Such a method is advantageous in that both sides of the document can be read using one reading unit, but is disadvantageous in that it takes significant time to read the both sides of the document.
A second method is reading both sides of a document by mounting a first reading unit to read a first side of the document and opposite a second reading unit to read a second side of the document. Such a method is advantageous in that the both sides of the document can be simultaneously read without unnecessarily circulating the document and thus a two-sided reading operation can be performed with high speed.
An example of the image reading apparatus employing the latter method is disclosed in Japanese Unexamined Patent Application Publication No. 2004-187144. The disclosed image reading apparatus includes first and second reading units respectively to read an upper side and a lower side of a document fed by an automatic document feeder. In a one-sided reading mode in which only one side of the document is read, the first reading unit reads the document and, in a two-sided reading mode in which both sides of the document are read, the first reading unit and the second reading unit read the document. Since the first reading unit is used in both the one-side reading mode and the two-sided reading mode, the first reading unit may be called a main reading unit which performs a main function when the document is read. Although the lifetime of the first reading unit is set to be equal to that of the second reading unit, the first reading unit 140 expires earlier than the second reading unit 150 because of the difference in work load.
However, since the conventional image reading apparatus is not built to take into account that the effective lifetime of the first reading unit is shorter than that of the second reading unit, the following problems may be caused. First, since the lifetimes of the first reading unit and the second reading unit expire at different points in time, it is cumbersome for a user to repair each reading unit whenever the replacement of such is necessary. Thus, the user may distrust the quality of the product.
If the document is read using the second reading unit which has been used less frequently than the first reading unit, better reading quality can be obtained. However, since the document is read using the first reading unit which has been used more frequently than the second reading unit, reading quality may deteriorate. In addition, when both sides of the document are read, an image read by the first reading unit is different from an image read by the second reading unit in quality.